The present invention relates to sonar devices generally, and more particularly, to a sonar listening device which amplifies acoustic signals non-electronically using fluidic technology.
Heretofore, most underwater listening devices have employed conventional piezoelectric, electrostrictive and magnetostrictive transducers. Some examples of piezoelectric materials are quartz, ammonium dihydrogen phosphate, and Rochelle salt. Electrostrictive materials include barium titanate and lead zirconate titanate. Both piezoelectric and electrostrictive materials develop an electrical charge when placed under pressure. Magnetostrictive materials alter the magnetic field which surrounds them when under pressure. These properties have been obtained using various ceramic materials which are easily molded into useful shapes. For this reason, it is very common for hydrophones to employ ceramic transducers. Other types of transducers useful in sonar applications include fiber optic hydrophones and thin-film polymers.
Generally, these types of hydrophones require some type of mechanical deformation in order to produce a useable electrical (or optical) signal. This, in turn, limits their sensitivity. The typically weak signals which are generated must be electronically amplified and filtered before they can be analyzed, and the equipment necessary to accomplish these tasks is both expensive, bulky, and delicate. Furthermore, in the case of low frequency signals, large apertures or diaphragms are necessary, thereby causing increased drag and flow-noise when in use.
Typical configurations for sonar sensors include the sono-buoy, the conformal array, permanently placed sensors such as SOSUS, and dipped or towed sonar. In any configuration it is desirable that the sonar listening device be sensitive, quiet, inexpensive, yet dependable. In the case of dipping sonar in particular, it is necessary that the sonar equipment be compact, as it must fit within a helicopter prior to deployment.